Hello, I have looked around forums and haven’t seemed to catch anything about how to implement an articulated Robotic Arm with Ardusub.Not just a grippier.
Before ordering the whole Pixhwk/ardusub system, I am trying to understand and figure out what it would be the most covnenient way to pair a 5 or 6 axis arm on my ROV project.
If ardusub is preconfigured for this, where do I plug the servowires onto (the navigator?).
Do I need to make my own code or I can use ardusub, if yes, at which conditions?
Thanks support in advance
Hi @kostantin, welcome to the forum 
This sounds like an interesting project! 
ArduSub does not currently have any articulation motor controls built in, and does not contain any inverse kinematics or input commands for a robot arm. The existing gripper support is handled as a single servo-style motor output, which is only used for opening/closing the end effector jaws.
Accordingly, you’ll need to write your own code. This could be implemented as an addition to the ArduPilot codebase (which ArduSub uses a subset of), or the manipulator could have its own control electronics and just use ArduSub (or BlueOS) to send the abstract commands to the arm (e.g. via I2C).
The only multi-axis robot arm I’m aware of for underwater vehicles at this size range is the Reach Alpha.
The Navigator and Pixhawk are both flight controller boards - they do similar things, and are not expected to be used together in the same vehicle.
If you choose to implement your arm control within ArduSub, it’s worth noting that the Navigator has 16 PWM outputs (which include those for the thruster outputs) compared to the Pixhawk’s 14 (which include the thruster outputs, and generally have one assigned to be used as a leak sensor). ArduSub-based ROVs most commonly have 6 or 8 thrusters, and I expect the additional stability and motion axes from 8 thrusters organised like in our BlueROV2 heavy configuration would be recommended for a use-case that involves a robot arm.
Hey, thanks for your answers. It’s not easy to plan such an arm without having in my hands the necessary hardware. And I wouldn’t end up making a purchase to realize that it was not a viable option. So let me say it with my own words, to make sure that I begin to understand the best course of action.
The “Navigator” would allow me to plug 5 or even 6 servos, to send signal and “Dedicated” power to the ARM ( that by the way it would need about 8V minimum). That being said, I should program (in C#Script hopefully) the necessary code for each of the 6 servos following the logic of Potentiometer VS analog gamepad: The actual movement of the servos should be triggered by the available buttons of a generic Gamepad. I might need a verbal conversation to clear all my questions. If any kindred spirit is willing to reach such a generosity, please let me know. There is teams,skypeor whatever, considering that I live somewhere in The United Arab Emirates (zulu+4). Best regards and thanks again
Hello, thanks for your previous answers. I have developed my prototype of 3 axis robotic arm. ANd I am using a PWM dc brushless servo attached to aux ports rc9 10, and 11 (aux 1,2 and 3). like in photo.
initially it looks to work fine and I was tuning the servo parameters like min and max values for servo 9,10 and 11 which corresponds to port 1, 2 and 3. But the results were odd and not responding really well, the serve were behaving not as expected, kind of not predictable.
this is the servo type
Please let me know what I am missing, or what additional component I am missing if able. Thanks
this is the servo specs:
Brand Name:
ROVMAKER
Model Number:
YS-Motor-008
Usage:
ROV
Type:
SERVO MOTOR
Torque:
15kg.cm
Brushless
Waterproof
40 Kg Digital Servo
Pulse Width Range:
500~2500 μsec
Peak Torque:
3.5N.m
Control Signal: PWM
hi @kostantin
I have done something similar with the same servo to open and rotate the gripper. At the moment it works fine, but I haven’t been able to test it for a long period of time.
I have not written any code, I have used the camera roll function in the aux 4, if I remember correctly, to rotate the arm with the underwater servo (I’ll check it in case I’m wrong)
The arm has a piece that allows it to be taken out, put in and bent or straight.
I attach photos:
Video:
Best regards
Andrés
After querying the factpry who made the servos, it seems that the slow death of all 3 servo motors was due to the DC dc stepdown converter, who probably was fluctuating and not maintaining a firm voltage of current. This unstable flow probably was the cause. As soon as I receive the replacement parts and test it again, I can be sure that the reason was related to the DC covnerter (those that you manually adjust to the desired voltage). Instead the factory will send me a preregulated DC stepdown.
Hi, I apologize for replying to such an old post, but I’m curious about where you guys bought the Rovmaker servos. I’ve seen them listed on several different Chinese websites, but I’m unsure which ones to trust. Also, how long was the delivery time?
Regards, Søren
Now you could easily put a Virpil style joystick on the end of the control arm giving you control over wrist rotation, gripper pressure, arm speed. Servos filled with mineral oil to take pressure at depth, magnetic hall-effect potentiometers replacing the carbon film ones for reliability. Currently building such a setup.